fix(review): address feedback from reviews 2788, 2789, 2791

- Move nodeCount increment after cycle detection to avoid over-counting
  cyclic references (sonnet #2)
- Use underscores in test case names used as filenames (sonnet #3)
- Fix function comment: 'prevent silent data loss' → 'prevent confusing
  behavior where additional documents are silently ignored' (sonnet #4)
- Mark design doc pseudocode as historical since implementation uses
  goccy/go-yaml ast.Node, not gopkg.in/yaml.v3 yaml.Node (sonnet #5)

review/persona_test.go

@@ -491,9 +491,9 @@ func TestYAMLEmptyFileRejection(t *testing.T) {
 		name    string
 		content string
 	}{
-		{"completely empty", ""},
-		{"whitespace only", "   \n\n  "},
-		{"comment only", "# just a comment\n"},
+		{"completely_empty", ""},
+		{"whitespace_only", "   \n\n  "},
+		{"comment_only", "# just a comment\n"},
 	}
 
 	for _, tc := range tests {